1) Field of the Invention
The present invention relates to a process for producing hydrophilic fibers with a water-insoluble inorganic substance. More particularly, the present invention relates to a process for producing hydrophilic fibers modified with a substantially water-insoluble inorganic substance, for example, a substantially water-insoluble metal hydroxide, precipitated in and fixed to bores, pores and surfaces of the hydrophilic fibers, to provide modified hydrophilic fibers useful as a paper-forming material, a shaped article-forming material, and other functional materials in which the specific functions of the substantially water-insoluble inorganic substance carried by the hydrophilic fibers are utilized.
2) Description of the Related Art
Various processes for producing hydrophilic fibers, for example, paper-forming pulp fibers, modified with a substantially water-insoluble hydroxide, for example, aluminum hydroxide, are known from Japanese Examined Patent Publication No. 56-18,712, which discloses a process wherein fine particles of aluminum hydroxide are adhered to surfaces of a paper sheet by a coating method; from Japanese Unexamined Patent Publication No. 57-144,754, which discloses a process wherein a paper sheet containing 70% by weight or more of aluminum hydroxide is formed from a pulp slurry containing an aluminum hydroxide powder; and from Japanese Unexamined Patent Publication No. 57-171,799, which discloses a process wherein a paper sheet containing 50 to 95% by weight of aluminum hydroxide is produced from a pulp slurry containing an aluminum hydroxide powder together with a sizing agent and binder.
In these conventional processes, the substantially water-insoluble inorganic substance are adhered in the form of fine particles to a surface of a paper sheet, or mixed in the form of fine particles to provide a pulp slurry, but a water-soluble inorganic compound is not utilized to provide the substantially water-insoluble inorganic substance.
As conventional methods wherein a water-soluble inorganic substance, for example sodium aluminate, is utilized for paper-making, Chizhov, G. I. et al., Mezhvuz, Sb. Mauch. Tr., Khimiya Tekhnol. Tsellyulozy, No. 8, 67-70 (1981) discloses a use of sodium aluminate mixed to a pulp, to enhance a mechanical strength of the resultant paper sheet; U.S. Pat. No. 3,706,629 discloses an addition of a polymeric electrolyte and an aluminate of an alkali metal to a pulp, to improve the dehydration property and retention of the pulp in the paper-forming step; and Canadian Patent No. 964,808 teaches an addition of a water-soluble aluminum salt and sodium aluminate to a pulp.
Nevertheless, these conventional methods do not teach a conversion of a water-soluble inorganic compound to a substantially water-insoluble inorganic substance on or within a hydrophilic fiber.
Lagally, P. and Lagally, H., Tappi, 42 (11), 888 (1959) teach a method of precipitating a gel-like aluminum hydroxide on pulp fibers by immersing the pulp fibers in an aqueous solution of sodium aluminate and neutralizing the sodium aluminate aqueous solution with a mineral acid, but this method is disadvantageous in that, since the mineral acid is added to the pulp slurry containing sodium aluminate, a major portion of the resultant gel-like aluminum hydroxide remains in the pulp slurry but not in and on the pulp fibers, and thus the utilization efficiency of the resultant aluminum hydroxide for the pulp fibers is poor.
This method is intended to increase the mechanical strength of the resultant paper sheet by the combination of the gel-like aluminum hydroxide with the cellulose pulp fibers, but the amount of the gel-like aluminum hydroxide picked up by the pulp fibers is relatively small, and thus the increase in the mechanical strength of the resultant paper sheet is unsatisfactory.
A method similar to that mentioned above is disclosed by Hechler E., Wochenblatt fur Papierfabrikation, 96 (23/24), 868 (1968). In this method, a beaten pulp slurry is supplemented with sodium aluminate in an amount of 5% based on the weight of the pulp, and then brought into contact with carbon dioxide, aluminum sulfate or calcium carbonate, to convert the sodium aluminate in the pulp slurry to aluminum hydroxide and thereby provide a filler-containing pulp usable for paper-formation.
This method, however, is disadvantageous in that the effective utilization efficiency of the resultant aluminum hydroxide is unsatisfactory.
Further, J. G., Soluble Silicates, ACS Monograph Series, Reinhold, N.Y., Vol. 2, 333 (1952) discloses a method in which sodium silicate (soluble glass) is added to a pulp slurry and the pH of the resultant sodium silicate-containing pulp slurry is lowered, to cause the resultant silicic acid gel to be precipitated. The purpose of this method is to size the resultant paper sheet with the silicic acid gel, and therefore, the amount of the silicic acid gel picked up by the pulp fibers must be relatively small.
Cray, W. L., Pulp and Paper Magazine of Canada, August, 116 (1955) discloses a process in which a pulp slurry is supplemented with calcium chloride and then with sodium silicate to produce calcium silicate in the pulp slurry, and thereafter, aluminum sulfate is added to the pulp slurry to cause the resultant calcium sulfate to be precipitated in the pulp fibers in the slurry.
This process, however, is not suitable for causing a large amount of a water-insoluble inorganic substance to be carried on the pulp fibers.
Japanese Unexamined Patent Publication No. 62-144,901 discloses a process in which two different types of water-soluble inorganic compound aqueous solutions, which form a water-insoluble and flame-resistant inorganic compound when mixed together, for example, an aqueous solution of barium chloride and boric acid and an aqueous solution of hydrogen ammonium phosphate and boric acid, is proposed; a wood material is immersed in one of the above-mentioned aqueous solutions and then in the other aqueous solution, to cause the resultant water-insoluble and flame resistant inorganic compound to be dispersed and carried in the wood material. This method is effectively produces a flame-resistant wood material, but is not suitable for modifying a hydrophilic fibrous material usable for paper.
Accordingly, it is not as yet known how to impart and fix a large amount of a substantially water-insoluble inorganic substance to hydrophilic fibers, for example, paper-forming pulp fibers.